The motor vehicle sector is one field of application where control units are used to control various tasks in a vehicle, such as fuel injection, throttle valve movement, control of servomotors (for example, wipers, air-conditioning flap valves, etc.). The reference to this field within the framework of the description of the present invention in no way limits the present invention thereto, but is merely intended for exemplary purposes.
To be able to effectively operate modern vehicles, various vehicle tasks are realized by a number of control units having suitable sensor inputs, control algorithms and actuator outputs. A plurality of steps are entailed in developing these types of control units for the automotive sector.
When defining a control engineering task, it is first necessary to mathematically model and simulate a technical-physical process upon which a desired dynamic behavior is to be impressed. On the basis of the resulting abstract mathematical model, various control concepts, which are likewise provided exclusively as a mathematical model conception, are able to be tested in the framework of numerical simulations; this step constitutes the modeling and controller design phase, for the most part on the basis of computer-based modeling tools.
In a second step, the controller designed in the mathematical model is transferred onto a simulation unit capable of real-time processing, which, for the most part, by far exceeds a typical production control unit, both in its computing capacity, as well as in its I/O capabilities, and which communicates interactively with the real physical process, respectively with a device that determines this process.
Since the transfer of the abstractly formulated controller from a modeling tool onto the simulation unit is largely automated, one speaks in the second phase of rapid control prototyping (RCP) or of function prototyping.
If the control engineering problem is resolved by the controller operated on the simulation unit, the control algorithm is then transferred in the context of the control unit implementation—mostly in a fully automated process—onto the production control unit that is to be ultimately used in practice. This process is described as implementation.
In principle, a pre-engineered control unit is now available, and test runs and test procedures could, therefore, be carried out at this point. Such test runs/procedures are carried out under unfavorable and extreme conditions in order to ensure fault tolerance. Since vehicle prototypes are usually not yet available at the time of this development stage, and to make parallel development possible by shortening development times, test scenarios are carried out on simulators.
This means that the developed real control unit inclusive of the software is tested on the basis of a simulated controlled system, respectively a test environment. This development step is referred to as a hardware-in-the-loop (HIL) process. Another advantage of such an approach is that a single control unit or only parts of the interconnected system of control units or also real components (for example, the motor) is/are also able to be simulated in combination with the control unit. This makes possible virtual test runs, long before the first vehicle prototype is complete. Enormous savings in costs and time are thereby achieved. Such a simulator is also able to perform test runs beyond the limits that real vehicles are capable of. In addition, test runs can be reproduced, automated and modified in terms of the parameters.
The controlled system, respectively a test environment can be simulated both on the software side, as well as by hardware. However, not every behavior can be readily simulated, particularly not that of an electrical or electronic load, so that the real load is then connected to the control unit. The throttle valve or also a wiper motor are mentioned here as examples.
In a simulation, inductive loads pose particular difficulties since, when the voltage supply is switched off, the inductance attempts to maintain the power in the system and thereby induces a current IL in the opposite direction of the supply current.
From the related art, it is known to simulate electrical/electronic loads using suitable hardware components that are brought onto load or installed. In the process, the real load, thus, in concrete terms, a wiper motor, for example, is connected in order to analyze the various aspects of the behavior. In this case, this hardware has a specific physical property, respectively a consistent physical behavior at the control unit, so that, a change in conditions necessitates connecting different hardware to a control unit.
This has the drawback that it is often necessary to reconfigure or modify the real loads. Accordingly, such systems are not readily scalable. Most notably, it is difficult to realize high current loads at low production costs.
Attempts to simulate the behavior of the electrical/electronic loads using computer-based simulation models are unsuccessful in simulating the dynamic behavior of real loads. To be able to simulate the dynamic behavior of a load to an adequate degree, execution times of less than one microsecond are necessary, such an execution time meaning the unit of time required for a one-time execution of a simulation model. Simulation models that are purely computer-based, such as in the simulation environment “Simulink” of the firm MathWorks, reach execution times of 100 microseconds.